Silicon carbide is considered a superior candidate material for high temperature, high power and high frequency electronic devices due to its high melting point, relatively large energy bandgap, high saturated electron drift velocity, breakdown field, high thermal conductivity and chemical resistance. Its large energy bandgap also makes it an excellent material for the blue light-emitting diodes and radiation intensive environments.
Silicon carbide exists in hexagonal, rhombohedral and cubic crystal structures. Generally, the cubic, zinc blende form is referred to as "Beta-SiC" whereas the numerous polytypes of the hexagonal and rhombohedral forms are collectively referred to as "Alpha-SiC." The most common Alpha form is 6H SiC.
Beta-SiC is usually considered more desirable than Alpha-SiC for the aforementioned electronic applications since its electron mobility is postulated to be higher than that of Alpha-SiC over the temperature range of 300 to 1000 K. Furthermore, the growth temperatures of Beta-SiC are generally lower than those of Alpha forms for various types of growth, for example chemical vapor deposition (CVD). However, the difficulties in the growth of high quality, low carrier concentration Beta-SiC thin films do not allow the electron mobility to attain these postulated values. This is believed to be due to the defects present in Beta-SiC films, especially those grown on Si substrates. Dislocations, stacking faults and antiphase domain boundaries (APBs) are generated from the Beta-SiC/Si interface and extend from the interface to approximately 3 .mu.m into the bulk film. In fact, many even propagate up to the as-grown surface. This phenomenon is caused by the differences in the lattice parameters (.about.20%) and thermal expansion coefficients (.about.8% at 473 K.) between the substrate and film. Although off-axis Si (100) substrates have been employed to help eliminate APBs, the dislocations and stacking faults remain. When Alpha-SiC substrates are utilized for the growth of Beta-SiC, device quality films have been obtained, but defects persist in the form of double positioning boundaries (DPBs).
The growth of 6H SiC films on 6H SiC substrates via CVD has been reported since the late 1960's. Several researchers reported the growth of 6H SiC on 6H SiC (0001) in the temperature range of 1500.degree.-1750.degree. C., but a mosaic morphology was observed on the as-grown surface. Such a mosaic structure is believed to be caused by DPBs. The growth of 6H SiC in the temperature range of 1320.degree.-1590.degree. C. was also reported, in which case, the growth direction was perpendicular to the [0001] axis. However, growth of 6H SiC in this direction while rapid, is quite irregular and results in unacceptable defect levels and surface morphologies.